The present invention relates generally to automated detection and alerting to the presence of hidden structure. More particularly, it provides a low-cost, fully integrated, mobile, early warning system for continuous detection and early warning of bridged crevasses. For certain applications, it may be solar powered with battery backup, with an option for at least one battery to be solar rechargeable.
Bridged crevasses present a challenge and hazard to parties traversing ice streams and glaciers in the Antarctic, the Arctic and elsewhere. While an open crevasse is usually visually discernible and therefore avoidable, there is little or no visual cue to the presence of a bridged crevasse or to the thickness of the overlying snow bridge. When in terrain where there is probable occurrence of bridged crevasses, progress is inhibited; parties remain roped together and travel slowly and deliberately. Personnel are at risk of injury or death if a snow bridge is unwittingly breached. Secondarily, loss of vehicles, sleds and equipment may occur.
The current state-of-the-art for bridged crevasse detection, warning, and spatial parameter quantification consists of two methods. Probing is a low-tech solution requiring a securely roped individual to carefully approach a suspected snow bridge and repetitively insert a long, thin wand deep into the snow, feeling for an underlying void. This xe2x80x9cdipstickxe2x80x9d approach can provide an approximate indication of the thickness of a snow bridge and the horizontal extent of the underlying abyss. The second method is an application of ground penetrating radar (GPR). This application has been discussed in the literature and has seen limited use in several forms for many years. Recent applications of this technique have been quite successful in locating bridged crevasses in the path of over-snow vehicles. The conventional GPR alternative, typically using a research-grade radar system, is hi-tech, expensive, requires a trained operator to interpret, and thus is used less frequently. In a typical application, a GPR antenna is positioned on a long boom ahead of the traversing vehicle or party. Electromagnetic pulses are transmitted in a broad antenna lobe pattern having vertical and some near-horizontal components. These pulses reflect from underlying snow and firn density boundaries, i.e., a boundary indicative of a dielectric contrast, and refract from the near-vertical walls of proximate crevasses. The boundary between the snow, firn or ice, and the air-filled void of the crevasse provides a strong dielectric contrast and reflector and refractor of electromagnetic energy. The typical radar signature (return) of snow and firn stratigraphy 100 devoid of crevassing is a series of nearly horizontal layers appearing as horizontal traces 102 below the surface 101 on a profile image as shown in FIG. 1. If a crevasse is encountered, the crevasse radar signature 200 is displayed as a convex hyperbolic curve 202, the apex being directly over the crevasse and the xe2x80x9ctailsxe2x80x9d trending deeper into the snowpack as shown in FIG. 2. FIG. 3 annotates the xe2x80x9ccrevasse signaturexe2x80x9d 200 of FIG. 2 with a dashed line 301 to delineate the crevasse. Note that this crevasse signature 200 is intermixed on the display with the stratigraphic signature 100 depicted in FIG. 1.
Conventional GPR operation while traversing suspect snow and ice fields employs a trained operator constantly observing a radar display to discern the hyperbolic crevasse signatures 200, halting traversal as the convex hyperbolic curve 202 appears on the display. This important activity is manpower intensive and is subject to a high fatigue factor with resultant dire consequences if not carefully monitored. Automating bridged crevasse proximity detection and warning using a low-cost designed-for-purpose radar system has positive implications for safety, economics and efficiency. It may be applied to scientific, search-and-rescue, industrial and commercial trans-glacial traversing in the Antarctic, the Arctic, and elsewhere.
A preferred embodiment of the present invention provides an automatic, portable, inexpensive, designed-for-purpose, crevasse detection system that is easy to operate and may be applied to field party and general snow field traversal scenarios to include diverse activities such as identifying the snow cave of a polar bear for investigation by a wildlife biologist.
An inexpensive system integrates the front-end of a commercial-off-the-shelf (COTS) ground-penetrating radar, a COTS personal computer (PC), and a specialized algorithm to alert to geospatial anomalies in real time. The alert may be aural, indicating the relative proximity of a geospatial anomaly. The system may also include a visual alert that indicates the relative proximity of a geospatial anomaly, or both an aural and visual alert.
In a preferred embodiment, the geospatial anomaly of interest is a crevasse, in particular, a bridged (hidden) crevasse. The bridge may result from accretion of snow, ice, firn, or any combination thereof.
In a preferred embodiment, the radar front-end is an FM-CW radar front-end, comprising an antenna (although multiple antennas may be used), a transceiver incorporating a circulator, a local oscillator, and a mixer.
In a preferred embodiment, the processor is a personal computer that incorporates at least a low pass filter (LPF), a high pass filter (BIF), an analog-to-digital (A/D) converter, a digital signal processor (DSP), and a display, such as a CRT or a liquid crystal display (LCD). For aural alerts, the PC further incorporates a sound card connected to at least one speaker.
The specialized algorithm processes returns from operation of the radar front-end in A and B parallel channels to establish a running average of vectors in the A channel for comparison to each single vector being processed currently (and concurrently) by B channel, such that the comparison permits detection of a spatial anomaly within a target volume illuminated by the radar front-end.
Also provided is an inexpensive method of detecting spatial anomalies within a target volume, the anomalies not otherwise evident without use of methods that are expensive, time-consuming, or both. A preferred embodiment of the method comprises:
illuminating a target volume with electromagnetic energy;
using circuitry to derive audio frequencies representing reflections of the electromagnetic energy;
establishing vectors representing the audio frequency versions of the reflected energy in A and B parallel channels, such that a running average of the vectors is maintained in channel A for comparison to a current vector being processed in channel B; and
using this comparison to initiate an alert.
The cost of equipment for this processing is minimized through down conversion to audio frequencies prior to processing.
In a preferred embodiment, the anomalies are voids otherwise hidden from observation. Of particular interest are voids representing crevasses hidden by accretion of snow, ice, firn, and any combination thereof. Methods are provided to provide an alert aurally, visually, or as a combination of both.
Aural alerts are established by processing scaled signals in parallel to establish the frequency and volume of the aural alert. Visual alerts are established by:
subtracting the running average vector of channel A from the current vector processed in channel B;
filtering the result of the subtracting to remove spikes that cause xe2x80x9cspeckle;xe2x80x9d
stacking by m, a whole number, the filtered result to achieve a stacked value,
clipping the stacked value to eliminate any amplitude variability that may introduce adverse effects;
peak extracting the clipped stacked value to establish a bin number for it, the bin number providing an estimate of distance to a nearest edge of the spatial anomaly;
using the bin number to drive a visual alarm function; and
displaying a visual alarm.
There are several advantages to a preferred embodiment of the present invention:
self-monitoring standoff geospatial anomaly detection;
useful for establishing a database of common stratigraphy types;
reduced workload and stress on detection system operator(s);
automated detection of geospatial anomalies, including bridged crevasses;
automated visual and aural alarm upon detection of a geospatial anomaly;
inexpensive to implement;
uses COTS hardware;
uses commercially available software;
suitable for applications such as determining archaeological sites of importance prior to employing heavy machinery for road building or construction;
easily reconfigurable for updating or use in other applications;
easy to learn, thus reduced training time and shortened learning curve;
increased speed of traversing surfaces of unknown stability;
facilitates search and rescue operations;
reliable;
easily maintained; and
durable.
For a lightweight, inexpensive embodiment that may be mounted on a PC board, the antenna may be any of: a stripline antenna, a stripline beam antenna, a Yagi stripline beam antenna, and a log periodic array (LPA) stripline beam antenna. The simplest embodiment for this antenna is a printed circuit wide-band xe2x80x9cbow-tiexe2x80x9d dipole antenna.
Preferably, the processing sub-assembly includes analog circuitry connected to the transceiver sub-assembly through a mixer. This analog circuitry conditions output signals from the mixer for digital processing. Digital circuitry receives conditioned output signals from the analog circuitry, converts it to digital format, and employs a complex algorithm for identifying geospatial anomalies such as a bridged crevasse or a snow cave. Display and alerting devices receive output from the digital circuitry to indicate the geospatial anomaly and provide a required alert.
In a preferred embodiment, the analog circuitry includes a first amplifier for amplifying the signal products from the mixer, a low pass filter (LPF) that passes only those frequencies that correlate to a pre-specified range, a second amplifier for amplifying the output of the LPF and a high pass filter (HPF).
The digital circuitry includes an analog-to-digital (AID) converter for converting the output of the high pass filter, a digital signal processor (DSP) for performing a Fast Fourier Transform (FFT), and a audio-visual display. The DSP implements a complex algorithm providing input to at least two methods of alerting, visual and audio.
If used with a robot, the system may further include a communications device including a UHF or VHF radio link, or a system providing an autodialer, a cellular phone and a cellular phone antenna. The frequency band of the radar system must be significantly displaced in frequency from the transmit frequency of any communications frequency (radio telemetry) to prevent interference between the radar and communication link and visa versa. To facilitate passing data, the radar signal may be converted from electrical to optical and passed from the radar transceiver to the data acquisition computer via an optical fiber. Preferably, all system components noted above are enclosed within a weatherproof enclosure.
In one embodiment, the system includes it own power source. The power source may include a solar panel augmenting a rechargeable battery. Further, a preferred embodiment may include its own boom and mounting bracket. In addition to the system itself, a unique method of implementing a geospatial anomaly detection capability is provided.
Provided is a method for detecting geospatial anomalies that may otherwise be hidden from view or other inexpensive means of detection. It comprises mounting a system of the present invention approximately level with a surface such as the surface of a snow field at a pre-selected look angle in azimuth and elevation; providing power to the system; illuminating at least part of a target volume with a signal containing electromagnetic energy; receiving energy reflected from the target volume as a result; processing the reflected energy together with a reference signal sampled from the transceiver to produce a difference frequency signal representing the difference in frequency between the reference signal and the reflected energy; establishing a value of the difference frequency signal; processing any non-zero value difference signals by implementing a complex algorithm; and using the output of the algorithm, collecting background data as a running average, and providing notification of any occurrence of the pre-specified geospatial anomaly. The notification, at least in part, may be audio, visual, or both.
A preferred implementation uses an antenna in direct contact with the surface e.g., snow or ice, and positioned at nadir (directly downward). Other embodiments may use slight xe2x80x9cslant anglesxe2x80x9d to gain some marginal standoff distance advantage.
In a preferred embodiment, an autonomous geospatial anomaly detecting and alerting system is provided in which components of the system as described above are mounted on a single printed circuit (PC) board. The existence of a pre-specified range of frequencies is correlated to an expected geospatial anomaly such as may be representative of a hidden void, for example.
Ground penetrating radar has long been used for archeological and utility location purposes. While the basic radar hardware design of an embodiment of the present invention could be used for those purposes, the crevasse-location algorithm is specific to detection of void anomalies in snow, ice and glacier fields. Other algorithms may be developed and xe2x80x9ctunedxe2x80x9d for these other applications although these applications present a more difficult problem and are not pursued as an application of the present invention. A glacial snowfield presents a fairly benign target volume for ground penetrating radar with few anomalies present internally. In the general condition of penetrating the earth, however, there are boulders, debris, and buried manmade objects that display, possibly confusing the snowfield-specific crevasse-detecting algorithm of the present invention.
An embodiment of the system may be powered by any of a number of sources including a source remote from its location and a backup source.
In one embodiment, a preferred embodiment of the present invention is mounted on a boom at the front of a mobile platform (to include a self-powered vehicle, a remotely piloted vehicle, a robot, or even a mammal) that is proceeding toward a target volume to be observed such as bridged crevasse or snow cave. The target volume may be remote from the controller of the mobile platform. The controller may also be mobile, thus a wireless communications device may be provided in one embodiment. A reference signal, fsource, is transmitted from the antenna towards the target surface. Resultant reflected radiation, i.e., the xe2x80x9cbackscatteredxe2x80x9d portion, is mixed with a portion of the transmitted signal sampled for that purpose. This mixing produces a difference frequency, fDif, which is then processed to distinguish internal structure of the target volume.
Digital circuitry implementing a complex algorithm establishes the presence of a geospatial anomaly within the target volume. Using a complex algorithm, the anomaly is identified and an alert displayed both visually and aurally. Upon such determination, the system may send a notification, preferably over a wireless communications device, to a platform controller at a remote location.